Process for reduction of inorganic contaminants from waste streams

ABSTRACT

The invention relates to the use of used alumina to reduce the level of inorganic contaminants, such as mercury and arsenic, from waste fluid streams. The invention further provides a process for reducing the level of mercury or arsenic in fluid streams by contacting the fluid stream with used alumina, such as used Claus catalyst.

This invention was made with Government support under CooperativeResearch and Development Agreement (CRADA) 0190-00, awarded by the U.S.Environmental Protection Agency. The Government has certain rights inthis invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the use of chemical sorbents to reduce thelevels of contaminants from waste streams. In particular, the inventionrelates to the use of used alumina, enriched with sulfur, to reduce oreliminate inorganic contaminants, including, but not limited to heavymetals or D-block metals, from waste streams. More particularly, theinvention relates to the use of used alumina to reduce the levels ofmercury and arsenic from waste streams.

2. Background of the Invention

Industrial pollutants such as heavy metals, D-block metals, mercury andarsenic pose significant health-related risks to the public. Forexample, several metal ions and transition metal ions have beenassociated with asthma symptoms such as activation of mast cells andenhanced allergen-mediated mast cell activation. Walczak-Crzewiecka, etal. “Environmentally Relevant Metal and Transition Metal Ions EnhanceFcε RI-Mediated Mast Cell Activation,” Env. Health Perspectives 111(5)(May 2003). Because these substances are generated as a by-product ofindustrial processes, it is important to find effective means to reducetheir release into the environment.

For example, mercury emissions from coal-fired utilities, commercialboilers and solid waste incinerators represent a serious environmentalproblem and have been the focus of many regulatory deliberations. TheClean Air Act Amendments of 1990 (Tit. 1H, § 112(b)(1)) require majorsources to use maximum available control technology to reduce mercuryemissions. The United Nations has considered binding restrictions on theuse of mercury through its environment program and has announced that itwill begin to assist countries in developing methods for reducingmercury emissions. Lacey, M., “U.N. Conference Backs Efforts to CurbMercury Pollution,” NY Times (Feb. 10, 2003). At present, coal-firedpower plants emit the largest source of mercury emissions at 32.7%.Municipal waste incinerators and non-utility boilers each contributeapproximately 18% of mercury emissions. Medical waste incineratorscontribute 10% of mercury emissions.

Mercury exposure has been associated with neurological and developmentaldamage in humans. Developing fetuses and young children are atparticular risk of the harmful effects of mercury exposure. In a reportprepared for Congress, the Environmental Protection Agency (“EPA”)identified mercury as a particular danger to public health. Among otherhealth-related concerns, the report identified increased levels ofmercury in the blood of women of childbearing age. “Mercury Threat toChildren Rising, Says an Unreleased EPA Report,” Wall St. J., Feb. 20,2003, A1. Mercury contamination is also a concern for populationsexposed to dental practices or dental waste, clinical chemistrylaboratories, pathology laboratories, research laboratories,chlor-alkali facilities, and health care waste incinerators.

To address these concerns, the EPA proposed regulations that wouldrequire reductions in mercury emissions from coal-fired power plants.EPA Press Release, Dec. 14, 2000. In addition, legislation has beenproposed that would cut mercury emissions by 50% by 2010 and by 70% by2018. Wall St. J., Feb. 20, 2003. However, despite the desire to reducemercury emissions, presently there are no commercially availabletechnologies to control mercury emissions. Id.

Similarly, exposure to arsenic poses potentially significant healthrisks. Arsenic is a natural element, distributed throughout the soil andin many kinds of rock. Because of its ubiquitous presence, arsenic isfound in minerals and ores that contain metals used for industrialprocesses. When these metals are mined or heated in smelters, thearsenic is released into the environment as a fine dust. Arsenic mayalso enter the environment from coal-fired power plants and incineratorsbecause coal and waste products contain some arsenic. Once arsenicenters the environment, it cannot be destroyed.

Arsenic exposure causes gastrointestinal problems, such as stomach ache,nausea, vomiting, and diarrhea. Arsenic exposure can also yielddecreased production of red and white blood cells, skin changes that mayresult in skin cancer, and irritated lungs. Inorganic arsenic has beenlinked to several types of cancer and is classified as a Group A, humancarcinogen. In high amounts (above about 60,000 ppb in food or water),arsenic may be fatal. Because of the serious adverse health effectsrelated to arsenic, in 2001, the EPA issued regulations limiting theamount of arsenic in drinking water to 10 parts per billion. 66 FederalRegister 6976.

Similar adverse effects have been associated with other inorganiccontaminants such as cadmium, chromium, lead, and selenium. Cadmium, forexample, is associated with chronic kidney, liver, bone and blooddamage. Like mercury and arsenic, cadmium occurs naturally in metal oresand fossil fuels; industrial releases of cadmium are due to wastestreams and leaching of landfills. Another contaminant, chromium, isassociated with such long-term effects as damage to liver, kidney,circulatory and nerve tissues, as well as skin irritation. The level ofchromium in drinking water is regulated by the Safe Drinking Water Actof 1974. Chromium is released to the environment through chemicalmanufacturing and combustion of natural gas, oil, and coal. Lead isanother contaminant associated with negative health effects, such asbrain and nerve damage in children, behavior and learning problems, andreproductive problems. Lead is released to the environment throughvarious industrial processes.

Various carbon-based sorbents have been identified for removing mercuryvapor from gas streams. T. R. Carey and C. F. Richardson, “AssessingSorbent Injection Mercury Control Effectiveness in Flue Gas Streams,”Environmental Progress 19(3):167-174 (Fall 2000). For example,Selexsorb® HG (Alcoa World Alumina, LLC, Pittsburgh, Pa.) and Mersorb®(Nucon International, Inc., Columbus, Ohio) are commercially availablecarbon-based mercury sorbents. Recycled tires have also been identifiedas a source of activated carbon that could be used for mercury removal.C. Lehmann et al., “Recycling Waste Tires for Air-Quality Control,”January 2000. Activated carbon has many drawbacks for use in large-scaleindustrial processes, however. In particular, commercially availableactivated carbon is a relatively expensive sorbent. Althoughtransformation of waste tires into activated carbon is anenvironmentally friendly means of recycling harmful waste, it is acomplicated, lengthy, energy-intensive and time-consuming process.Additionally, the yield of activated carbon from waste tires isrelatively low.

Thus, there is a need for new technologies to efficiently andcost-effectively reduce the level of inorganic contaminants, such asmercury and arsenic for example, in industrial emissions.

Activated alumina is a well-known sorbent. Industrial applications foractivated alumina include: natural gas processing, dryers and forming,ethylene processing, petroleum refining, air separation, catalystsupport, hydrogen peroxide manufacturing, and water treatment. Aluminahas applications in ceramics, refractories, refining, abrasivematerials, glass, cerments and powder metallurgy, electricalapplications, coatings, fibers, metallizing, and gas dehydration.

As used herein, “used alumina” is a by-product of a chemical orindustrial process that enriches the alumina with sulfur orsulfur-containing compounds. A significant source of used alumina is theClaus process, which is used to recover elemental sulfur from hydrogensulfide in gases. Industrial applications of the Claus process include,without limitation, steel production, oil refineries and natural gasrefineries. Activated alumina is used as a catalyst in the Clausprocess. As more sulfur is deposited onto the activated alumina throughthe Claus process, the material loses its catalytic ability and becomes“spent” or “used.”

Used alumina represents a significant source of industrial waste.Approximately 50,000 to 75,000 tons of used alumina are generatedannually. Regeneration of used alumina, such as Claus catalyst is anexpensive process, however. Because it is economically disadvantageousto regenerate the used alumina, much of the used alumina ends up inlandfills. Thus, there also exists a need to recycle used alumina intoother useful applications.

SUMMARY OF THE INVENTION

The inventors have discovered unexpected and surprising characteristicsof used alumina. In particular, it has been discovered that used aluminathat is enriched with sulfur is a particularly effective sorbent forreducing levels of inorganic contaminants from fluid streams.Nonlimiting examples of contaminants that can be reduced using usedalumina are heavy metals, D-block metals, chalcogens, Group 15 metals,mercury, arsenic, chromium, cadmium, lead, and selenium.

In one aspect, the invention provides a process for removing mercuryfrom waste streams using used alumina. Thus, the invention provides auseful means of recycling a material that is otherwise consideredindustrial waste. Moreover, by employing a recycling process, theinventive process provides significant cost savings over traditionalmethods that use commercially prepared sorbents used to removepollutants from waste streams. For example, commercial sorbentsSelexsorb® (Alcoa) and Mersrob® (Nucon) cost between five and sevendollars per pound, whereas the cost of used alumina recovered from theClaus process is less than one dollar per pound. In some embodiments,the sulfur-enriched alumina of the invention is effective at removingboth ionic mercury and elemental mercury from industrial waste streams.

In one embodiment, the invention provides a process for reducing thelevel of an inorganic contaminant from a fluid stream by contacting thefluid stream with used alumina. In another embodiment, the inventionprovides a process for reducing the level of an inorganic contaminantfrom a fluid stream including the following steps: (1) flowing the fluidstream through a bed containing a sorbent that includes used alumina;(2) sorbing, either by adsorption or absorption, the inorganiccontaminant from the fluid stream onto the surface of the sorbent; and(3) allowing the contaminant-depleted effluent stream to exit from theoutlet of the bed. Nonlimiting examples of inorganic contaminantsinclude: heavy metals, D-block metals, chalcogens, Group 15 metals,mercury, arsenic, chromium, cadmium, lead, and selenium. In someembodiments, the fluid stream is gaseous. In other embodiments, thefluid stream is liquid. In yet further embodiments, the mercury is ionicor elemental.

In one embodiment, the invention provides a process for reducing thelevel of mercury from a fluid stream by contacting the fluid stream withused alumina. In another embodiment, the invention provides a processfor reducing the level of mercury from a fluid stream including thefollowing steps: (1) flowing the fluid stream through a bed containing asorbent that includes used alumina; (2) sorbing mercury from the fluidstream onto the surface of the sorbent; and (3) allowing themercury-depleted effluent stream to exit from the outlet of the bed. Insome embodiments, the fluid stream is gaseous. Gaseous fluid streamsinclude, without limitation, those as a result of the burning ofbituminous coal or Powder River Basin and lignite coal. In otherembodiments, the fluid stream is liquid. In yet further embodiments, themercury is ionic or elemental.

In a further aspect, the invention provides a process for removingarsenic from fluid streams using used alumina. In one embodiment, theused alumina is used Claus catalyst. In another embodiment, theinvention provides a process for reducing the level of arsenic from afluid stream including the following steps: (1) flowing the fluid streamthrough a bed containing a sorbent that includes used alumina; (2)sorbing arsenic from the fluid stream onto the surface of the sorbent;and (3) allowing the arsenic-depleted effluent stream to exit from theoutlet of the bed. In some embodiments, the fluid stream is gaseous. Inother embodiments, the fluid stream is liquid. In yet furtherembodiments, the arsenic is ionic or elemental.

DESCRIPTION OF THE FIGURES

FIG. 1 is a graphical representation of the thermogravimetric analysis(TGA) of used alumina sample AA-191, as described in Example 6.

FIG. 2 is a graphical representation of the thermogravimetric analysis(TGA) of used alumina sample AA-199, as described in Example 6.

FIG. 3 is a graphical representation of the thermogravimetric analysis(TGA) of used alumina sample AA-222, as described in Example 6.

FIG. 4 is a graphical representation of the thermogravimetric analysis(TGA) of used alumina sample AA-246, as described in Example 6.

FIG. 5 is a graphical representation depicting the percent removal of 10ppm mercury from 1 g of various sorbents, as described in Example 8.

FIG. 6 is a graphical representation depicting the percent removal of 10ppm mercury from 0.1 g of various sorbents, as described in Example 8.

DETAILED DESCRIPTION

The patent and scientific literature referred to herein establishesknowledge that is available to those with skill in the art. The issuedpatents, applications, and references that are cited herein are herebyincorporated by reference to the same extent as if each was specificallyand individually indicated to be incorporated by reference. In the caseof inconsistencies, the present disclosure will prevail.

For purposes of the present invention, the following definitions will beused:

Definitions

The term “about” is used herein to mean approximately, in the region of,roughly, or around. When the term “about” is used in conjunction with anumerical range, it modifies that range by extending the boundariesabove and below the numerical values set forth. In general, the term“about” is used herein to modify a numerical value above and below thestated value by a variance of 20%.

The terms “used alumina” and “spent alumina” are used interchangeablyherein to refer to alumina that is a by-product of a chemical orindustrial process that enriches the alumina with sulfur orsulfur-containing compounds. In one nonlimiting example, one form ofused alumina is a by-product of the Claus process, which uses activatedalumina as a catalyst for removing or isolating sulfur. “Used alumina”or “spent alumina” is contrasted with virgin alumina, which has not beensubjected to a chemical process. Thus, used alumina may contain higherlevels of sulfur compared to virgin alumina.

The terms “sorbent,” “sorb,” “sorption” and their variants are usedherein to refer to a substance that absorbs, adsorbs, or entrapssomething; the act of absorbing, adsorbing, or entrapping; or theprocess of absorbing, adsorbing, or entrapping. As used herein, theseterms are not intended to be limited to a particular mode of entrapment,such as absorptive, adsorptive or other phenomena.

The invention provides processes for reducing the level of inorganiccontaminants in fluid streams (e.g., gaseous or liquid) using usedalumina. Nonlimiting examples of contaminants that may be reduced usingthe processes of the invention are heavy metals, D-block (i.e.,transition) metals, chalcogens, Group 15 metals, mercury, arsenic,chromium, cadmium, lead and selenium. More particularly, the processesof the invention may be used to reduce the level of mercury and arsenicin fluid streams.

Without wishing to be bound by a particular theory, the inventorstheorize that the unique bonding characteristics of sulfur make it aparticularly good substance for interacting with a variety ofcontaminants. Sulfur has the ability to bond directly to all elementsexcept the noble gases and nitrogen gas or liquid. Greenwood, N.N. andEarnshaw, A., “Chemistry of the Elements,” Pergamon Press, (1984) at782-783. Sulfur also has the ability to act as a ligand (i.e., anorganic moiety off a metal center) and as an electron donor which allowsit to react directly with a metal to form a S—M (metal) bond. Theliterature describes certain complexes which involve a sulfur moleculebonded directly to a metal center. Many amino acids are derivitized witha sulfur functionality and thus can bond with metals or enzymes. Forexample, hemoglobin utilizes a sulfur functionality. Therefore, it isbelieved that used, sulfur-enriched alumina is an effective sorbent forcontaminants that have favorable sulfur-bonding characteristics.

In one aspect, the invention provides a process for reducing the levelof mercury in fluid streams (e.g., gaseous or liquid) using usedalumina. Applications of the invention in liquid systems include,without limitation, instrument manufacturing, gold mining, fluorescentlamp manufacturing and recycling, dental wastewater, chlor-alkaliprocess, water purification, coal-fired utility scrubber washers andaqueous streams. Applications of the invention in gaseous systemsinclude, without limitation, coal-fired power plants, natural gas,hydrogen, and air purification.

In some embodiments, at least about 50% of the contaminant is removedfrom the fluid stream. In other embodiments, at least about 75% of thecontaminant is removed from the fluid stream. In still otherembodiments, at least about 90% of the contaminant is removed from thefluid stream.

In some embodiments, at least about 50% of mercury is removed from thefluid stream. In other embodiments, at least about 75% of mercury isremoved from the fluid stream. In still other embodiments, at leastabout 90% of mercury is removed from the fluid stream.

In another aspect, the invention provides a process for reducing thelevel of arsenic from a fluid stream using used alumina. In oneembodiment, the used alumina is used Claus catalyst. In one embodiment,at least about 50% of arsenic is removed from the fluid stream. Inanother embodiment, at least about 75% of arsenic is removed from thefluid stream. In still another embodiment, at least about 90% of arsenicis removed from the fluid stream. In other embodiments, the arsenic iselemental arsenic. In further embodiments, the arsenic is ionic arsenic.

The amount of contaminant that is removed is also measured on a basis ofthe amount in a given time period. For example, in one nonlimitingembodiment, between about 10-100% of the contaminant is removed from thefluid stream within about 0.25-24 hours. In another embodiment, betweenabout 10-100% of the contaminant is removed within about 1.5-2.5 hours.In still another embodiment, about 10-100% of the contaminant is removedwithin about 0.25-1.5 hours. In a further embodiment, about 10-100% ofthe contaminant is removed within about 1-24 hours. In otherembodiments, about 95% of the contaminant is removed within about 1-24hours. In another embodiment, about 60% of the contaminant is removedwithin about 1-24 hours. In still another embodiment, about 25% of thecontaminant is removed within about 1-24 hours. In yet anotherembodiment, about 40% of the contaminant is removed within about 1-24hours.

The contaminants that are decreased using the methods of the inventionmay be in elemental or ionic form. For example, in one embodiment, whenusing the processes of the invention to reduce the levels of mercury influid streams, the mercury is in the form of mercuric chloride. Inanother embodiment, the mercury is in the form of mercury nitrate. In afurther embodiment, the mercury is in the form of elemental mercury(e.g., oxidation state is Hg⁰). Similarly, other contaminants removed bythe methods of the invention may be in elemental or ionic form.

The used alumina sorbent is introduced into the fluid stream as anaerosol or by aspiration, or on beads, as powders, or support on amembrane to facilitate removal of inorganic contaminants. In someembodiments, the sorbent is configured in a free-floating manner; inother embodiments, the sorbent is in a packed bed configuration. Instill other embodiments, the sorbent is mixed with other materials inthe sorbent bed. Non-limiting examples of such other materials include:other sorbents, silica or sand, glass wool, or molecular sieves. Thefluid stream containing the inorganic contaminant is passed through theused alumina sorbent to facilitate reduction of the contaminant in thestream. In some embodiments, contaminant reduction is furtherfacilitated by arraying the alumina in parallel configuration (i.e., thefluid stream is split into a series of parallel streams, each of whichis associated with a sorption zone, each containing used alumina). Inother embodiments, reduction is facilitated by arraying the alumina inseries configuration (i.e., the fluid stream is passed through a seriesof successive sorption zones, each containing used alumina).

In one aspect, the process for reducing the level of inorganiccontaminants in fluid streams comprises the steps of (a) flowing thefluid stream through a bed containing a sorbent that contains usedalumina; (b) sorbing the inorganic contaminant from the fluid streamonto the surface of the sorbent; and (c) allowing the effluent stream toexit from the outlet of the bed. The size and configuration of thesorbent bed will vary, depending on the specific application. Theappropriate bed system depends on the specific application and isreadily ascertainable by those skilled in the art. For example, thesteps for contaminant removal depend on the configuration of the flowstream, the temperature within the flow, and the flow rate.

In one nonlimiting example, a fixed bed contactor with an inlet andoutlet is filled with used alumina. Nonlimiting examples of fixed bedcontactors are columns and cartridges. The fluid stream is directedthrough the inlet end of the contactor through a piping system or otherappropriate system, readily determinable by persons skilled in the art.As the fluid stream passes through the contactor containing the usedalumina, the metal contaminant (e.g., mercury, arsenic, chromium,cadmium, etc.) is sorbed onto the surface of the alumina, therebyreducing the level of contaminant present in the fluid stream. The fluidstream is then allowed to exit the contactor through the outlet aseffluent.

In some embodiments, the effluent stream is captured and recycled forother purposes or for further processing. In other embodiments, wherecontaminants are sufficiently removed from the fluid stream, theeffluent is released to the environment or is recycled for other uses.

In addition to bed contactors, other removal systems, well-known tothose of skill in the art, may be used to reduce the level of inorganiccontaminants from fluid streams. In one embodiment, the used alumina isinjected directly into the fluid stream. In this method, the usedalumina is crushed into finely divided particles and droppedcounter-current to the fluid stream. In one nonlimiting example, theparticle size of the used alumina is fine enough to create an aerosol.In other nonlimiting examples, the alumina particles form a mist or acloud. In some embodiments, the alumina is introduced to the fluidstream by injection or aspiration through a cylindrical collar that isplaced in the fluid stream. As the alumina passes through the fluidstream, inorganic contaminants (e.g., mercury, arsenic, chromium,cadmium, etc.) sorb onto the surface of the alumina, thereby reducingthe level of the contaminant from the fluid stream that has passedthrough the sorption zone created by the used alumina. A capturemechanism is then used to isolate and remove the mercury-containingalumina particles. Capture mechanisms are well-known to those of skillin the art. In one nonlimiting example, electrostatic particles (ESP)are used as a capture mechanism.

In another embodiment, the bag-house method is used to reduce the levelof inorganic contaminants. This method is known to those of skill in theart. Briefly, in this method, used alumina is loaded into a bag-house, apermeable membrane container. Before being loaded into the container,the alumina is pulverized to a small particle size. The bag-house isplaced in the flow of a fluid stream (e.g., a gaseous stream). As thefluid passes through the used alumina contained in the bag-house,inorganic contaminants contained in the stream are sorbed by thealumina.

In yet another embodiment, a batch contacting method is used to decreasethe level of inorganic contaminants in fluid streams. In thisembodiment, a predetermined amount of used alumina is placed in a volumeof fluid. The fluid-alumina mixture is allowed to reach equilibrium, atwhich point no further inorganic contaminant will be removed from thefluid. In some embodiments, the mixture is agitated to hastenequilibrium. In other embodiments, the pH of the solution is adjusted tooptimize contaminant removal. In one nonlimiting example, the pH of themixture is adjusted to between about pH 4 and about pH 5.5. In yetfurther embodiments, the pH of the fluid is adjusted by adding nitricacid or an acid of similar acidity. The period for reaching equilibriumvaries, depending on the size of the container, the capacity of the usedalumina, the mass of the used alumina, the concentration of thecontaminant, the amount of sulfur species on the alumina, and thespecies and type of contaminant being sorbed. For example, in someembodiments, when removing mercury from a fluid stream, thefluid-alumina mixture is agitated for between about 0.25 hours and about48 hours. The used alumina is then separated from the fluid. In onenonlimiting embodiment, the used alumina is separated using filtration.In another nonlimiting embodiment, the used alumina is separated usinggravity filtration. If the contaminant level of the fluid has notreached an acceptable level, successive batches are exposed to thealumina, in the manner described above.

The conditions under which the removal process is operated are adjustedfor optimal reduction of the contaminant of interest. The conditionsselected for optimization, as well as the range of each condition, willvary depending on the mode of the process (e.g., liquid or gas) and arewell within the knowledge of those skilled in the art. Nonlimitingexamples of operating conditions that are adjusted for optimal reductioninclude: pH, flow rate, temperature, residence time, flow mode, andamount of sorbent. The skilled artisan will recognize that eachcondition can be adjusted individually or in any combination with otherconditions.

In some embodiments, the pH of the fluid stream is acidic, e.g., aboutpH 0-7. In another embodiment, the pH of the fluid stream is about pH2-6. In a further embodiment, the pH of the fluid stream is about pH2-4. In some embodiments, the pH of the fluid stream is basic, e.g.,about pH 7-10. In some embodiments, the pH of the fluid stream isaltered to achieve a particular pH range, while in other embodiments,the pH is “ambient”, meaning it is unadjusted (i.e., the pH of thestream is its pH after the step immediately preceding the removal stepof the invention). Methods for adjusting the pH of the fluid stream arewell-known to those of skill in the art. Nonlimiting examples of suchadjustment methods include: addition of base to increase pH or additionof acid to lower pH. Examples of suitable bases include, withoutlimitation, NaOH, NH₄OH, Ba₂OH, KOH, and Ce(OH)₄. Examples of suitableacids include, without limitation, HCl, H₂SO₄, HNO₃, acetic acid, H₃PO₄,HClO₄, formic acid, HBr, HI, NH₂SO₃H.

The flow rate of the fluid stream is also adjusted in some embodimentsto optimize the reduction of the contaminant(s). In one embodiment, theflow rate is about 0.5-1 L/min. In another embodiment, the flow rate isabout 0.75-1.25 L/min. In a further embodiment, the flow rate is about1.25-1.5 L/min. In yet another embodiment, the flow rate is about 1L/min. In a still further embodiment, the flow rate is about 1.4 L/min.

In some embodiments, the temperature of the fluid stream is adjusted tooptimize reduction of the contaminant(s). In one embodiment, thetemperature is ambient. In another embodiment, the temperature is about5-200° C. In another embodiment, the temperature is about 5-25° C. In afurther embodiment, the temperature is about 20-50° C. In yet anotherembodiment, the temperature is about 50- 100° C. In still anotherembodiment, the temperature is about 100-200° C. In yet a furtherembodiment, the temperature is about 140° C.

In some embodiments, the residence time is adjusted to optimizereduction of the contaminant(s). In some embodiments, the residence timeis about 1 second to about 48 hours. In other embodiments, the residencetime is about 1 hour to about 24 hours. In further embodiments, theresidence time is about 1 hour to about 12 hours. In still otherembodiments, the residence time is about 1 second to about 1 hour. Inone embodiment, the residence time is about 0.05-1 second. In anotherembodiment, the residence time is about 0.05-0.25 second. In a furtherembodiment, the residence time is about 0.25-0.5 second. In yet anotherembodiment, the residence time is about 0.5-1.0 second. In someembodiments, the residence time varies with the temperature of the fluidstream. For example, in one nonlimiting embodiment, the residence timeis about 0.23 second at about 23° C. In another nonlimiting embodiment,the residence time is about 0.17 second at about 140° C.

The flow mode of the invention is also varied depending on theconditions of the process. In some embodiments, the flow mode isvertical, i.e., downflow. In other embodiments, the flow mode ishorizontal.

The amount of used alumina added to the sorbent bed is also varied tooptimize the process of the invention. In one embodiment, about 0.1-100%of the sorbent bed is composed of used alumina. In another embodiment,about 0.1-1% of the bed is composed of used alumina. In a furtherembodiment, about 1-25% of the bed is composed of used alumina. In yetanother embodiment, about 25-50% of the bed is composed of used alumina.In a still further embodiment, about 50-75% of the bed is composed ofused alumina. In another embodiment, about 75-100% of the bed iscomposed of used alumina. In situations where the sorbent bed iscomposed of less than about 100% used alumina, nonlimiting examples ofmaterials comprising the remaining fraction of the sorbent bed includeother sorbents, silica or sand, glass wool, and molecular sieve. Othermaterials known to those of skill in the art are also contemplated bythe invention.

The used alumina of the invention may be any alumina recycled from achemical or industrial process, in which the alumina is enriched withsulfur. In one non-limiting example, the sulfur-enriched used alumina isused (or recycled) Claus catalyst. In the Claus process, activatedalumina is used as a catalyst to remove sulfur-containing compounds fromfluid streams. Sulfur compounds react on the alumina surface to produceS₂ and water. Claus catalysts can be doped with SiO₂, Fe₂O₃, Na₂O, TiO₂,or Group VIB or VII metals. The alumina is rendered inactive, or“spent,” when the alumina becomes rehydrated, or when the pores of thealumina become sulfated due to oxygen entering the system. At thispoint, the catalytic ability of the catalyst decreases. In someembodiments, the sulfur present in the used alumina catalyst is in theform of S₄, which most likely adheres to the alumina in the form ofaluminum sulfate. In other embodiments, the sulfur is present in theform of sulfites or sulfones. In still more embodiments, elementalsulfur is present as a deposit on the surface of the alumina.

In some embodiments, the used alumina undergoes one or more processingsteps before being used as a sorbent for inorganic contaminants (e.g.,before the used alumina is loaded on the bed or into the sorbent zone).The processing steps expose a larger portion of the surface area of thealumina, thereby increasing the capacity of the alumina to sorbcontaminants. The processing steps are performed with used alumina(e.g., Claus catalyst) after it has been enriched with sulfur. Theprocessing steps increase the number of sorptive sites available on thealumina, thereby increasing its sorptive characteristics.

In one embodiment, the processing step includes crushing the alumina.Crushing the alumina increases the surface area of the particles,thereby exposing additional sorptive sites. Larger particle sizes areeffective for removing contaminants from liquid streams, whereas smallerparticle sizes (e.g., less than about 600 mesh or less than about 300mesh) are required to effectively remove contaminants from gaseousstreams. If the particles become too small, however, their sorptivecapabilities may be hindered or eliminated due to a decrease in theframework size of the particle. In one non-limiting example, the aluminais crushed to less than about one millimeter in diameter. In anotherexample, the alumina is crushed to less than about 0.5 millimeter. Inyet another example, the alumina is crushed to less than about 0.1millimeter. In still another example, the alumina is crushed to lessthan about 300 mesh. The particles are crushed using methods well knownto those of skill in the art. The appropriate method for crushing theused alumina particles is chosen based on the ultimate particle sizedesired. Nonlimiting examples of crushing methods include, withoutlimitation, a ball mill and mortar and pestle.

In another embodiment, the processing step comprises heating thealumina. In one nonlimiting example, the sulfur-enriched alumina isheated to less than about 600° C. In another nonlimiting example, thealumina is heated to less than about 500° C. The heating step drives offsurface moisture, carbon, and other volatile material from the alumina.The heating step also affects the surface area of the alumina, however.For example, the surface area of activated alumina is between about250-300 m²/g, while the surface area of calcined alumina is betweenabout 100-125 m²/g. Calcined alumina is achieved by heating alumina totemperatures greater than about 1200° C. Therefore, the heating stepshould be performed at temperatures sufficient to remove moisture andvolatile material, while avoiding conditions that would begin to affectparticle size.

In another embodiment, the processing step includes heating the usedalumina as described above, followed by crushing the particles, asdescribed above. In still another embodiment, used alumina is heatedthen crushed prior to being further enriched with sulfur.

Effective sorption of contaminants is related to the amount of sulfurspecies on or in the sorbent. Thus, the ability of the sorbent to removecontaminants from fluid streams is optimized by manipulating the sulfurcontent of the used alumina. For example, higher levels of sulfur relateto improved sorption characteristics for mercury removal. As shown inExamples 6 and 7, used alumina sample AA-191 (Metal Alloy Reclaimers,Inc. II, Cleveland, Ohio (“Metaloy”)), which has a sulfur content of22.5%, removed 36% of mercury after one minute. In comparison, sampleAA-222, which has an experimentally determined sulfur content of 1.5%,removed 24% of mercury after one minute. In contrast, sample AA-191removed only 58% of arsenic from a test sample containing 100 ppmarsenic, whereas sample AA-222 removed 95% of arsenic from a similarsample (Example 8). Therefore, in some embodiments, the sulfur contentof the alumina is in the range of about 1% to about 50%. In oneembodiment, the sulfur content is at least about 25%. In anotherembodiment, the sulfur content is at least about 2%. In still anotherembodiment, the sulfur content is no more than about 25%. In yet anotherembodiment, the sulfur content is at least about 0.1%.

The sulfur content of the used alumina is manipulated by methods knownto those of skill in the art. In one nonlimiting example, the mercuryremoval process employs used alumina “as is.” That is, the sulfurcontent of the used alumina is not altered through further processing.In another embodiment, the desired sulfur content of the alumina isachieved by adding sulfur (i.e., doping or enriching) to either used orvirgin alumina. Doping is achieved by methods well-known to thoseskilled in the art. One nonlimiting example of a doping method includespretreating the alumina followed by exposing it to a gas streamconsisting of hydrogen and sulfur-containing compounds. This methodincludes heating the alumina with nitrogen or an inert gas to remove airand dry the alumina. Once pretreatment of the alumina is achieved, thealumina is exposed to a gas stream that includes hydrogen andsulfur-containing compounds. Both hydrogen and sulfur must be present toconvert the oxides on the alumina to sulfides. Nonlimiting examples ofdoping agents include carbon disulfide (CS₂), dimethylsulfide (DMS),dimethyldisulfide (DMDS) and other organic sulfides.

In another embodiment, the sulfur content of the used alumina isdecreased by driving off excess sulfur. Sulfur removal is achieved bymethods known by those with skill in the art. One nonlimiting example ofa sulfur removal process is pre-reclaim burn, wherein the used aluminais heated in the presence of oxygen. Another method for reducing thesulfur content of used alumina is through dilution, a process by whichused alumina containing higher levels of sulfur is mixed with usedalumina containing lower levels of sulfur.

The dispersion characteristics of the sulfur on the surface of thesulfur-impregnated alumina are also correlated with improved contaminantsorption. For example, the inventors have observed that contaminantsorption is increased when the sulfur species is evenly distributed onthe surface of the alumina. Without wishing to be limited to aparticular theory, the inventors believe that when the sulfur species isclustered on the surface of the used alumina, the surface area availableto sorb the contaminant is decreased. Thus, although there may be agreater mass of sulfur species on the used alumina, sorption will bedecreased because of the lower surface area. Nonlimiting examples ofmethods to analyze dispersion characteristics are scanning electronmicroscopy, Brunauer Emmett Teller (BET) surface area analysis andporsimetry.

EXAMPLES Example 1 Removal of Mercury from Liquid (Aqueous) Samples

The removal of ionic mercury(II) using used alumina was demonstratedusing laboratory synthesized aqueous metal-tainted solutions. Thesolutions were prepared at two levels of mercury(II): 1 ppm and 10 ppm.Spent alumina samples (AA-199, AA-246, AA-222, AA-191, Metaloy) wereused as sorbents for the liquid phase experiments. These sorbents werereclaimed from Claus catalyst processes. Used alumina was first dried byplacing the sorbent in a drying oven, at 100° C. for approximately fourhours. After drying, seven samples of sorbent were weighed. The sampleswere 0.1 g, 0.25 g, 0.25 g (two samples for precision), 0.5 g, 0.75 g,1.0 g, and 1.5 g. The sorbent was added to the simulated waste sample(100 mL) and the contents of each bottle were manually swirled (1minute) to assure complete wetting of all of the sorbent. Two controlsamples were also prepared. The first control contained no sorbent. Thesecond control sample included virgin alumina that did not containsulfur. The pH of each bottle was measured and adjusted to approximatelypH 4.0 to approximately pH 5.5 with 1 M NaOH or 1M HCl, as needed. Thebottles were agitated for up to 24 hours, followed by filtration anddilution for sample analysis.

Approximately 2-3 mL of sample was removed from each bottle and thesorbent was filtered from the solution. In a reaction vessel, 1 mL ofsample was diluted to a total volume of 10 mL with 2% nitric acid. Onedrop of 5% potassium permanganate was added and the solution mixed. Athree percent sodium borohydride was introduced into the vessel,resulting in the formation of mercury vapors and hydrogen gas. Mercurylevels in the treated solutions were determined by cold vapor atomicabsorption (CVAA) spectroscopy. The gas and vapor was passed through anabsorption cell positioned in the path of the spectrophotometer. Astandard curve was prepared using known concentration solutions. Thecurve was fit using linear regression analysis. The mercuryconcentration of each of the test samples was calculated by comparingthe response obtained from the instrument to the standard curve.

The results are shown in Tables 1 and 2, below. These data are averageresults of multiple independent experiments for each alumina sample. Twoexperiments were performed for the 1 ppm sample. Four experiments wereperformed for the 10 ppm sample. Capacity is the amount of metal on thesorbent on a per gram of sorbent basis (mg of metal/g of sorbent). TABLE1 Average Removal of 1 ppm Hg²⁺ from aqueous stream (n = 2) Theo-retical % Removal [Hg²⁺]_(e) Capacity Lot Mass Average SD Average SDAverage SD AA-199 0.10 91.16 0.57 0.088 0.001 0.892 0.062 0.25 91.580.09 0.084 0.001 0.363 <0.001 0.50 93.70 2.03 0.063 0.020 0.189 0.0030.75 95.07 0.34 0.049 0.003 0.127 0.001 1.00 94.61 0.91 0.054 0.0090.095 0.001 1.50 95.48 0.59 0.045 0.006 0.064 0.001 AA-246 0.10 92.300.33 0.077 0.003 0.875 0.014 0.25 92.65 0.21 0.073 0.002 0.359 0.0220.50 93.17 0.37 0.068 0.004 0.186 <0.001 0.75 93.65 0.03 0.064 0.0010.125 0.001 1.00 94.27 0.50 0.057 0.005 0.094 <0.001 1.50 94.49 0.550.055 0.006 0.063 <0.001 AA-222 0.10 92.56 2.40 0.075 0.023 0.926 0.0110.25 99.23 0.22 0.008 0.002 0.398 0.002 0.50 99.51 0.04 0.005 <0.0010.199 <0.001 0.75 99.47 0.11 0.006 0.001 0.132 0.001 1.00 99.47 0.050.006 0.001 0.099 0.001 1.50 99.52 0.02 0.005 <0.001 0.066 <0.001 AA-1910.10 98.30 1.55 0.017 0.016 0.941 0.008 0.25 99.14 0.38 0.009 0.0040.398 0.005 0.50 99.38 0.09 0.006 0.001 0.199 0.001 0.75 99.37 0.050.006 <0.001 0.133 0.001 1.00 99.39 0.01 0.006 <0.001 0.100 0.001 1.5099.41 0.01 0.006 <0.001 0.066 <0.001

TABLE 2 Removal of 10 ppm Hg²⁺ from aqueous stream (n = 4) Theoretical %Removal [Hg²⁺]_(e) Capacity Lot Mass Average SD Average SD Average SDA-246 0.10 87.078 4.21 1.292 0.421 8.689 0.402 0.25 88.666 3.78 1.1330.378 3.544 0.117 0.50 83.109 12.81 0.939 0.384 1.807 0.078 0.75 93.1913.34 0.681 0.335 1.242 0.044 1.00 95.224 2.68 0.478 0.268 0.951 0.0251.50 98.685 0.98 0.132 0.098 0.658 0.006 AA-222 0.10 88.124 3.73 1.1880.372 8.766 0.123 0.25 95.419 3.10 0.458 0.310 3.795 0.132 0.50 99.0310.62 0.097 0.062 1.980 0.014 0.75 99.021 0.40 0.098 0.039 1.319 0.0091.00 98.873 0.22 0.113 0.022 0.989 0.002 1.50 98.373 2.46 0.163 0.2460.655 0.016 AA-191 0.10 89.887 2.63 1.019 0.267 8.806 0.219 0.25 96.8992.35 0.311 0.234 3.849 0.095 0.50 97.362 4.87 0.265 0.487 1.940 0.1020.75 99.766 0.07 0.023 0.007 1.328 0.001 1.00 99.798 0.04 0.021 0.0030.997 0.005 1.50 99.823 0.03 0.017 0.005 0.667 0.003 AA-199 0.10 90.1554.76 0.985 0.476 9.037 0.440 0.25 91.277 2.25 0.872 0.225 3.639 0.0960.50 94.231 2.25 0.577 0.225 1.887 0.042 0.75 95.262 1.32 0.474 0.1321.272 0.018 1.00 96.386 1.50 0.361 0.150 0.966 0.015 1.50 97.301 1.560.270 0.156 0.649 0.010

These data confirm that as little as 0.1 g/mL of used alumina iseffective at removing as much as 10 ppm of mercury from aqueous wastesamples. Moreover, because the mercury content in the control samples(containing no alumina) did not decrease, these experiments demonstratethat the loss in mercury is a result of the sorption phenomenon and notdue to precipitation. The effectiveness in removing mercury from thesamples increased slightly as more sorbent was added, but was stilleffective at the lower levels. In addition, the inability of the virginalumina control samples to decrease the mercury levels in the samplesconfirms the sorption is due to the presence of sulfur on the usedalumina.

Example 2 Removal of Mercury from Gas Samples

In this prophetic example, used alumina (Claus catalyst) sorbents willbe screened using an on-line mercury analyzer, which allows monitoringof outlet mercury concentration from the reactor in real time, therebyreducing the extensive number of tests that need to be performed inorder to determine when equilibrium has been achieved. Because theoxygen present in simulated flue gas interferes with the on-lineanalysis, the screening will be performed using either nitrogen or argoncarrier gas. The sorbents will be tested in range of 70° C. and 150° C.The amount of mercury sorbed on the sorbents will be determined by CVAAspectroscopy, by leaching the mercury off the sorbent.

After the initial screening tests, additional tests will be conductedusing simulated flue gas, which requires a batch sampling method usingimpingers (Ontario Hydro Method, known to those of skill in the art).Three tests at different contact time periods will be performed, toassure that equilibrium is obtained. The mercury will be dosed into thesystem by an apparatus that diffuses known concentrations of mercuryinto a system. The apparatus is a mercury-filled u-shaped tube. Apredetermined flow of gas will then be bubbled into the tube todistribute the mercury. The quantity of mercury being dosed into thesystem will be calculated based on the known vapor pressure of mercuryand the known flow rate.

Example 3 Removal of Mercury from Gas Samples—Experiment #2

General Procedure

In this prophetic example, an elemental mercury (Hg⁰) permeation tube(3cm, Vici Metronics, Inc) is used to steadily provide Hg⁰vapor into thesystem. The Hg⁰is introduced into the system using nitrogen at a flowrate of about 100 mL min⁻¹ as a carrier gas, which is passed over thepermeation tube. The carrier gas flow rate is maintained with the use ofa mass flow controller (MFC). Release of Hg⁰vapor at a rate of 91 ngmin⁻¹, (11 parts per billion by volume inlet Hg⁰ concentration) isachieved by immersing the permeation tube in a temperature-controlledwater bath (about 55.5° C.). The influent Hg⁰ vapor concentration isrepeatedly measured with 4% (w/v) KMnO₄/10% (v/v) H₂SO₄ impingersolutions.

Simulated flue gas is chosen from one of two types: bituminous coal andPowder River Basin (PRB), based on the type of coal that is present.Bituminous coal results in a higher percentage of oxidized mercury,while PRB coal results in higher percentage of elemental mercury. Thesimulated flue gas of PRB and lignite coals primarily consists of 3%(v)oxygen (O₂), 12%(v) carbon dioxide (CO₂), 7%(v) water (H₂O), 500 ppm byvolume sulfur dioxide (SO₂), 200 ppm by volume nitrous oxide (NO), and11 ppb by volume elemental mercury (Hg⁰) balanced with nitrogen (N₂)gas. For PRB, the simulated mixture is prepared by blending separatestreams of gases supplied from pressurized gas cylinders of 0.98%(v) SO₂in N₂, 4140 ppm by volume NO in N₂,a mixture of 80%(v) C₂ and 20%(v) O₂,and N₂ gas humidified via a flask containing water maintained at 47° C.to approximate a 7%(v) water vapor concentration. The flow rates of allof these gases are separately controlled by individual mass flowcontrollers (MFC). The total 1 L min⁻¹ at 23° C. of gas flow is suppliedto a fixed-bed reactor inlet through preheated Teflon lines with aheating tape to prevent water condensation. Then, the total streamenters the on-line mercury analyzer and its effluent gas stream iscaptured by an impinger train to analyze the mercury contents by a CVAAspectrophotometer.

Blank Experiments

Blank experiments are carried out to examine the sorption of mercuryvapor on the tubing, reactor, and blank glass fiber filter. The systemis cleaned with 10%(v/v) nitric acid and de-ionized water before eachexperiment to remove residual mercury in the system as described inSection 8.6.2 of the Ontario Hydro Method(http://rmb-consulting.com/download/ontariohg.pdf).

Analytical

An on-line Hg analyzer is used to obtain breakthrough curves and tostudy the dynamic sorption capacity of the tested sorbents. The analyzeris calibrated using the calibrated Hg⁰ permeation tube and the mercurydetection limit is determined. The analyzer is designed to detect onlyHg⁰ vapor in the gas stream, and cannot detect any oxidized mercuryportion. When mercury sorption tests are conducted in the system, theeffluent mercury can be fully or partially oxidized due to reactionsbetween elemental mercury, a sorbent, and other simulated flue gascomponents. Therefore, the oxidized mercury, if formed, is captured withan impinger containing either tris(hydroxymethyl)aminomethane (tris)solution or potassium chloride (KCl) solution prior to Hg ^(o) detectionusing an on-line mercury analyzer.

The tris solution method (Radian Corp.) has been shown to be effectivein capturing only oxidized mercury in other Electric Power ResearchInstitute (EPRI) studies. Carey, T. R.; Hargrove Jr., O. W.; Richardson,C. F.; Chang, R.; Meserole, F. B. Factors Affecting Mercury Control inUtility Flue Gas Using Activated Carbon. J. Air & Waste Manage. Assoc.1998, 48, 1166. The KCl solution is the first impinger set used in theOntario Hydro Method to determine oxidized mercury. Other gas componentsin the simulated flue gases such as SO₂, HCl, and H₂O are also known tointerfere with 253.7-nm ultra violet (UV) irradiation emitted from amercury lamp in the on-line mercury analyzer. Therefore, the gas passingthrough the tris or KCl solution flows through another sodium carbonate(Na₂CO₃) buffer solution to remove SO₂ and HCl from the effluent gasstream. The effluent gas stream goes through an empty impinger placed inan ice bath as a water trap before Hg ^(o) is finally detected with theon-line mercury instrument. Then, the total stream leaving the on-linemercury analyzer is captured by an Ontario Hydro impinger train toanalyze the mercury contents by the CVAA spectrophotometer.

Fixed-Bed Sorption Experiments

The used alumina is tested using the on-line mercury analyzer formonitoring the effluent Hg⁰, and an Ontario Hydro impinger train underthe simulated flue gas to validate the system performance. The sorbentsamples are mixed in silica diluent (SiO₂, Fisher Scientific, finegranules, particle size: 149-420 μm) prior to being packed in thereactor. About 20-30 mg of each sorbent in 6 g of silica is used and thebed material is supported by a fritted quartz disk with a Teflon o-ringand a glass fiber filter with a nominal 1 μm pore diameter in order tominimize channeling and prevent the escaping sorbent through the bed.Typical test conditions are summarized in Table 3, below. An additionalfilter system with a glass fiber filter with a nominal 0.7 μm porediameter is used at the outlet of the reactor to capture sorbentparticles potentially escaping from the bed. TABLE 3 Summary of testconditions Item Exemplary Test Conditions Reactor ½-in. (1.28 cm) i.d.borosilicate Temperature (° C.) 140 Flow rate (cm³/min) 1,000 @ 23° C.;1,395 @ 140° C. Flow mode downflow Superficial velocity 13 @ 23° C.; 18@ 140° C. in an empty reactor (cm/s) Residence time 0.23 @ 23° C.; in anempty reactor (s) 0.17 @ 140° C. Sorbent 20-30 mg in 6 g of a sand bedGas PRB/lignite simulated flue gas Inlet Hg⁰ concentration 91 ng/min =11 ppbv = 78 ppbw = 91 μg/Nm³ Sorption capacity Up to 90% totalbreakthrough; impinger determination solution analysis

During each test, the mercury-laden inlet gas bypasses the sorbent bedand is passed to the analytical system until the desired inlet mercuryconcentration is established. Then, the sorption test is initiated bydiverting the gas flow through the sorbent column in downflow mode tominimize the potential for fluidization of the bed. All of the tubingand valves in contact with elemental mercury are constructed fromTeflon, which has been demonstrated to have good chemical resistance andinertness toward elemental mercury. The sorbent bed and filter system isplaced in a temperature-controllable convection oven, which can maintainthe system temperature within 0.5° C. A Teflon coated thermocouple isinstalled in the fixed-bed reactor to control the gas temperature at theinlet of the sorbent bed.

When mercury speciation studies are conducted, an impinger trainemployed from the Ontario Hydro Method for collection of mercury samplesis placed on the outlet side of the system. The total gas flow rate ismonitored at the outlet of the impinger system using a bubble flowmeter.

Example 4 Dispersion of Sulfur on the Surface of Used Alumina

The dispersion characteristics of sulfur on the surface of used aluminawere investigated by scanning electron microscopy (SEM). Each sample wasground into a powder in an agate motor and pestle and then passedthrough a 600 mesh sieve to assure uniform sample size.

SEM analysis was performed on virgin alumina Maxcell 727 (PorocelAdsorbents, Catalysts & Services, Little Rock, Ark.) and UOP S-201 (UOPLLC, Des Plaines, Ill.) to establish a baseline for comparison with thesulfur-containing samples. Both materials are pure white powders. Thepore structure of Maxcell 727 was relatively open and exhibited only thealumina support; no surface species (sulfur) was detected. Compared tothe Maxcell sample, the pore structure of the UOP S-201 was not as open;it also did not exhibit a surface (sulfur) species.

SEM analysis was performed on four samples of used alumina, AA-222,AA-199, AA-246, and AA-191 (Metaloy). AA-222 exhibited tight porestructure, similar to UOP S-201. Small aggregates were observed on thesurface of the support. Elemental Diffraction Analysis (EDAX) indicatedthe presence of approximately >2% sulfur, based on counts per second.The EDAX data suggests that the aggregates observed in the SEM aresulfur species. AA-199 indicated the presence of approximately >2%sulfur, based on EDAX analysis. The SEM also showed the presence ofsulfur aggregates. AA-246 exhibited tight pore structure, similar to UOPS-201. The sulfur species was present at approximately >1% (EDAX). TheSEM showed fewer aggregates on the surface of the alumina compared tothe other samples. AA-246 also exhibited tight pore structure, similarto UOP S-201. The sulfur species was present at approximately 20%(EDAX). The SEM showed a uniform dispersion of sulfur aggregates in ahigher concentration than the other samples. The distribution of thesulfur in each of the Metaloy samples was ubiquitous and evenlydistributed on the surface of the alumina, regardless of the totalamount of sulfur present. The data are summarized in Table 3. TABLE 4Surface dispersion of sulfur on used alumina Sample Description EDAX SEMMaxcell 727 Pure white powder n/a No surface species UOP S-201 Purewhite powder n/a No surface species AA-222 Slightly gray powder  >2%Small aggregates AA-199 Pale white-gray powder  >2% Small aggregatesAA-246 White powder  >1% Almost no aggregates AA-191 Yellow powder;strong ˜20% Evenly dispersed sulfur odor aggregates

These data demonstrate that, while the quantity of sulfur may vary fromsample to sample, the sulfur deposited on the used alumina is uniform insize and distribution.

Example 5 X-Ray Powder Diffraction Analysis of Alumina

X-ray powder diffraction (XRD) was used to identify the type of surfacespecies present in used alumina samples from the Claus process. Thetechnique also determined if any phase changes of the alumina supportoccurred as a result of the Claus process.

Analysis was performed on powdered samples and mounted using theaccepted standard analysis technique. The sample is crushed to aconsistent size, no passing through a mesh is needed. The crushed powderis then introduced into a stainless steel holder using a backfillingtechnique. The backfilling allows the sample to be pressed into thesample holder which enables the sample to remain in place. Thebackfilling technique also increases the random order of the packing ofthe sample. The lamp sources of Cu-α and the scanning 2θ region was from10-70 degrees.

Analysis of UOP S-201 and Maxcell 727 did not indicate the presence of asurface species. The spectra were representative of the spectra foralumina oxide (Al₂O₃). The form was γ-alumina, with a small portion ofα-alumina. The two spectra were nearly identical, indicating the samephase of alumina, with major peaks at 28, 38, 43, 50, and 68 2θ values.

Two samples of amorphous activated carbon used for mercury sorption werealso analyzed as a comparison. Mersorb® (Nucon) and Selexsorb® (Alcoa)where each showed a sharp spike at 27 2θ, which appeared to becrystalline and indicates the possible presence of a sulfide (S²⁻)species.

Four samples of used alumina were analyzed (AA-199, AA-222, AA-246, andAA-191, Metaloy). The spectra confirmed that these samples shared thesame phase-support as the two virgin materials, UOP S-201 and Maxcell727. These data confirm that no phase change of the alumina occurs dueto the Claus reaction and also that the sulfur is not incorporated intothe alumina framework.

An increase in intensity was observed among the used alumina samples,which is attributed to the presence of sulfur on the surface of thealumina. The spectra for all four samples were comparable, showing peaksat 28, 38, 43, 58 and 68 2θ. The particular sulfur species could only bedetermined for AA-191, which had significantly more sulfur content thanthe other samples. The relatively small amount of sulfur present in theother samples prohibited determination of sulfur species. Sample AA-191showed additional spikes at 23, 26, 28 2θ, which were further analyzedand determined to be the S₈ form of sulfur.

Example 6 Thermogravimetric Analysis of Used Alumina

Thermogravimetric analysis (TGA) was also used to determine the quantityof sulfur species on used alumina from the Claus process. In theexperiments, about 6-9 mg of sample was crushed into a powder andexposed to an oxygen environment. The sample was then heated at a rateof 20° C. per minute until the temperature reached 800° C. The sampleswere analyzed twice, once without pretreatment, and a second time withpretreatment which included heating for 24 hours at 110° C.

As a control, two virgin materials (UOP S-201 and Maxcell 727) wereanalyzed. Two samples of activated carbon sorbent, Mersorb® andSelexsorb®, were also included for comparison.

The TGA profiles of used alumina samples AA-199 and AA-222 (FIGS. 2 and3, respectively) were similar to those of the virgin material, whichdemonstrate a gradual decrease in mass over the temperature range. Thesedata confirm a lower quantity of sulfur present in these materialscompared to AA-246 and AA-191 (FIGS. 4 and 1, respectively), whoseprofiles were qualitatively different from the other samples. The TGAspectrum for AA-191 showed a sharp decrease in mass starting atapproximately 250° C. and ending at approximately 325° C. Sample AA-246also showed a decrease in this range, although the change was not assharp as observed for AA-191.

The low initial temperature loss (˜250° C.) demonstrates that the sulfurspecies is predominately physically sorbed to the surface of thealumina, most likely via Van der Waals and/or London Dispersion Forces.Chemical bonding of the sulfur to the alumina would result in higherinitial temperature loss (˜300° C.).

Example 7 Determination of Sulfur Content in Used Alumina Samples byElemental Analysis

Elemental analysis was performed on the used alumina samples, virginmaterial and activated carbon, to determine percent sulfur content. Thecalculations used in the analysis were adjusted because the system didnot afford complete combustion. First, it was assumed that the totalmass lost was the entire mass of the organics present on the sample(i.e., eliminating the sulfur present). Second, it was assumed that theonly organic moiety lost was sulfur, not carbon, hydrogen or oxygen.Because there was no coke formation on the used Claus catalysts, and theTGA analysis did not reveal the presence of other organic substances,this assumption was valid.

In the experiment, a known quantity of sample was introduced into thesample pan (weighing apparatus) on a section of aluminum foil. Afterweighing, the foil was crimped to encase the sample. The foil-encasedsample was then introduced into the heating chamber. The sample washeated to a temperature of 800° C. to insure complete combustion. Thefinal weight was also measured and the amount lost is the quantity whichwas lost. Samples were analyzed on a Perkin-Elmer Analyst 1100 Series.The data are provided in Table 5. TABLE 5 Elemental Analysis of UsedAlumina Samples Sample % Sulfur Maxcell 727 0.0 UOP S-201 0.0 AA-199 >1AA-246 1.8 AA-222 1.5 AA-191 22.5

These data confirm that sample AA-191 has the highest sulfur content ofthe used alumina samples. These data also confirm that the other usedalumina samples contain detectable quantities of sulfur.

Example 8 Sorption Experimentation

Sorption experiments were performed to determine the kinetics andcapacity for mercury removal of the used alumina samples. Two usedalumina samples, AA-191 and AA-222 were evaluated. Virgin alumina(Maxcell and UOP S-201) was analyzed as a control. The ability of theused alumina samples to remove mercury was compared to the carbonaceousmaterial, Mersorb and Selexsorb. A system control comprising a knownconcentration of mercury in water was also analyzed. This sample wasused to ensure that the disappearance of mercury was not attributed toprecipitation. There was no decrease in mercury concentration in thesesamples. Thus, the removal of mercury is not attributed toprecipitation.

The samples were exposed to a laboratory prepared solution containing 10ppm mercury(II). The experiments were performed as described above,Example 1. In one experiment, 0.1 g of sorbent was used. In a secondexperiment, 1.0 g of sorbent were used. The sorbent material waspowdered to allow for maximum surface area. The reaction was allowed toproceed for a period of time up to twenty-four hours, with samples takenat predetermined times to determine the reaction kinetics. During thereaction, the samples were shaken horizontally. The data are shown belowin Table 6 and FIGS. 5 and 6. TABLE 6 Sorption of Mercury using 1.0 gSorbent Time Max. Hg Needed to Sorbent % Removed Removed Max. RemovalReach Max. Material after 1 min. (ppm) Efficiency (%) Removal (min.)Maxcell¹ 0.0 2.60 29.2 1440 UOP S-201¹ 0.5 1.41 16.3 1440 Mersorb² 92.59.853 100 90 Selexsorb² 59.1 8.845 100 180 AA-191 36.1 10.4 100 90AA-222 23.5 5.8 54.7 1440¹Virgin alumina²Activated carbon sorbent

These data confirm the effective removal of mercury from aqueous samplesusing used alumina as a sorbent. These data also suggest that thekinetics of removal and the total capacity of the sorbent for removalincreases as the sulfur content increases in the material. The usedalumina sorbent used for this experiment, A-191 and A-222 containapproximately 20% and 2% sulfur, respectively. Mercury removal for theused alumina sorbent is comparable to the commercially availablecarbonaceous sorbents.

Example 9 Removal of Arsenic using Used Alumina as Sorbent

The removal of ionic arsenic(V) using used alumina was demonstratedusing laboratory synthesized aqueous metal-tainted solutions. Thesolutions contained 100 ppm and 1000 ppm arsenic(V) (Na-arsenate).Activated carbon sorbents, Mersorb and Selexsorb, were included forcomparison purposes. Virgin alumina samples UOP S-201 and Maxcell 727were included as controls.

Activated alumina was first dried by placing the sorbent in drying oven,at 100° C., for approximately 4 hours. After drying, 0.2 g of eachsorbent was weighed. The sorbent was added to 0.01 L of metal solutionand the contents of each bottle were manually swirled to assure wettingof all of the sorbent. When the arsenic concentration was 100 ppm, thepH was fixed at pH 7. When the arsenic concentration was 1000 ppm, thepH of the samples varied from pH 6.6 to pH 10.1. The bottles wereagitated for a period up to 24 hours. The temperature and final pH ofeach bottle was recorded before the samples were filtered and diluted.

The amount of arsenic remaining in each sample was determined byinductively coupled plasma (ICP) spectroscopy. Approximately 2-3 mL oflaboratory synthesized aqueous metal-tainted sample were removed fromeach bottle and the sorbent was filtered from the solution. In ananalytical vessel, 1 mL of sample was diluted to a total volume of 10 mLwith 2% nitric acid. The sample was then introduced to the ICP via aperistaltic pump and delivered as an aerosol into the plasma source. Theinstrument, a Perkin-Elmer 3000 ICP, then scanned a large series ofwavelengths to identify which elements were present. Each element has aspecific energy and is assimilated to a fingerprint. A calibration curveis assembled prior to analysis using four know concentrations and thepoint fit by linear regression. The instrument retains this curve andthen calculates the unknown's concentration using this curve. Theresults are shown below in Table 7, below. TABLE 7 Removal of Arsenic(V)% Arsenic(V) Sorbed Sample 100 ppm 1000 ppm UOP S-201 100 65 Maxcell 727100 65 Mersorb 24 50 Selexsorb 54 61 AA-199 100 71 AA-222 100 75 AA-246100 60 AA-191 62 62

These data demonstrate that used alumina is an effective sorbent forarsenic. These data also suggest that lower levels of sulfur present inthe sorbent result in improved sorption of arsenic.

While the foregoing invention has been described in some detail forpurposes of clarity and understanding, these particular embodiments areto be considered as illustrative and not restrictive. It will beappreciated by one skilled in the art from a reading of this disclosurethat various changes in form and detail can be made without departingfrom the true scope of the invention and appended claims.

1. A process for reducing the level of mercury from a liquid streamcomprising contacting said liquid stream with used alumina.
 2. Theprocess of claim 1, wherein the used alumina is used Claus catalyst. 3.The process of claim 1, wherein the used alumina has a sulfurconcentration of at least about 0.1-25% by weight.
 4. A process forreducing the level of mercury from a liquid stream containing mercury,comprising the steps of (a) flowing the liquid stream through a bedcontaining a sorbent, wherein the sorbent comprises used alumina; (b)sorbing mercury from the liquid stream onto the surface of the sorbent;and (c) allowing the mercury-depleted effluent stream to exit from theoutlet of the bed.
 5. The process of claim 4, wherein the used aluminais used Claus catalyst.
 6. The process of claim 4, wherein the usedalumina has a sulfur concentration of at least about 0.1-25% by weight.7. The process of claim 1 or claim 4, wherein the used alumina iscrushed prior to being loaded on the bed.
 8. The process of claim 7,wherein the used alumina is heated to remove moisture prior to beingloaded on the bed.
 9. The process of claim 1 or claim 4, wherein atleast about 50% of mercury is removed from said liquid stream.
 10. Theprocess of claim 1 or claim 4, wherein at least about 75% of mercury isremoved from said liquid stream.
 11. The process of claim 1 or claim 4,wherein at least about 90% of mercury is removed from said liquidstream.
 12. The process of claim 1 or claim 4, wherein the mercury iselemental mercury.
 13. The process of claim 1 or claim 4, wherein themercury is ionic mercury.
 14. A process for reducing the level ofarsenic from a liquid stream comprising contacting said liquid streamwith used alumina.
 15. The process of claim 14, wherein the used aluminais used Claus catalyst.
 16. A process for reducing the level of arsenicfrom a liquid stream containing arsenic, comprising the steps of (a)flowing the liquid stream through a bed containing a sorbent, whereinthe sorbent comprises used alumina; (b) sorbing mercury from the liquidstream onto the surface of the sorbent; and (c) allowing thearsenic-depleted effluent stream to exit from the outlet of the bed.